Project Summary In recent years the use of engineered nanomaterials (ENMs) has exponentially increased. These materials have been incorporated in new or developing technologies, and industries worldwide are using these nanomaterials as integrated sensors, semiconductors, drug delivery systems, structural materials, and components of sunscreens and cosmetics, clothing and children?s toys. The principal properties that differentiate ENM from other materials are increased relative surface area, and high quantum effects which can change or enhance several properties of the manufactured materials, including their reactivity, strength and electrical characteristics. However, these characteristics may also confer other detrimental properties related to their biological toxicity (high rate of pulmonary deposition and high inflammatory potency per unit mass, among others), which may lead to adverse health effects. Even though the number of ENMs entering the market is increasing every year, there is a lack of information regarding the degree and conditions in which workers and consumers are exposed to ENMs and their potential adverse health outcomes. In vitro studies conducted with carbon nanotubes and titanium dioxide nanoparticles have provided inconsistent results regarding toxicity. Differences in ENM aerosolization and sampling methods, exposure mechanism and dose, cell line and conducted cytotoxicity assays, contribute to these discrepancies in the results. However, the greatest challenges are associated with particle delivery (exposure mechanism) and dosimetry. In addition, common in vitro models use submerged cell cultures which is a simplistic representation of human lung. In recent years, more realistic cell cultures in the air-liquid-interface (ALI) have been used for assessing biological outcomes of airborne particles in general. As a result, aerosol exposure chambers, which culture and expose multiple ALI cells to aerosolized nanoparticles have been developed. Although these systems provide new tools to study the toxicity of airborne particles there are still many shortcomings (long exposure times, dosimetry characterization, reduced particle deposition in the nanometer size range, large size and heavy weight, etc.) that must be resolved before their wide-scale acceptance. Here we proposed the adaptation of a newly developed airborne particle delivery technology for efficient and reliable exposure of ALI cells to ENMs in both working and indoor environments.